This invention relates generally to ballast devices for lighter-than-air balloons, and particularly to a method and apparatus for achieving long duration, controlled hovering at equilibrium with a Mylar-type balloon.
Lighter-than-air balloons are well known to the art. Many types of balloons are used for novelty and entertainment purposes, the more common employing helium, hydrogen, or heated air to provide buoyancy or lift. The preferred toy balloon uses one to five cubic feet of non-combustible helium which may be supplied from a tank or canister, and has traditionally been manufactured from a thin rubber or latex sheet material having an elongated neck which may be tied to provide a closure for the balloon. The materials used for such balloons are somewhat porous to helium gas, and the balloons rapidly lose their buoyancy in air as the helium diffuses through the material. A standard toy balloon may retain buoyancy sufficient to counterbalance its own weight for a period ranging from a few hours to several days in the case of weather-type balloons.
One recent development in the art is the "Mylar" balloon, which uses a plastic sheet material coated or impregnated on one side with a thin layer of a metallic foil or coating. Such a structure is far less permeable to helium and other gases, and positive buoyancy can easily be maintained for many days with such a balloon. A representative example of such a balloon structure is disclosed in U.S. Pat. No. 4,077,588 to Hurst. The neck portions of these Mylar balloons are generally sealed using thermal or electrosonic welding, or they may be closed with an adhesive application such as shown in U.S. Pat. No. 4,547,168 to Blacksberg. Because the Mylar balloons have much lower internal gas pressure than conventional rubber balloons, and because the internal gas diffuses more slowly, the reduction in buoyancy over time more closely resembles a linear relationship having a very gradual slope as compared to that for conventional rubber balloons.
The ability to maintain positive buoyancy in a balloon over long periods of time has invariably resulted in people attempting to attain a controlled equilibrium or hovering condition, and to sustain that "aerostatic" flight for as long as possible, rather than resorting to tethering the balloon. This permits the balloons to be left on display for extended periods of time, or used in games and recreational activities such as shown in U.S. Pat. No. 3,611,623 to Copstead. Mylar balloons have become very popular as gift items, with personal messages and greetings being printed on the face of the balloon, and for advertising or promotional devices.
The art contains many methods and apparatuses designed to achieve and maintain static equilibrium flight, as well as to simulate larger-scale flying devices such as hot air balloons or dirigibles. Some recent examples of these ballast devices may be seen in U.S. Pat. Nos. 4,145,838 to Mason; 4,356,661 to Calderwood; and 4,758,199 to Tillotson.
However, as the buoyancy of the balloon decreases due to loss of helium, the weight of the ballast and balloon will eventually exceed the buoyant lift of the gas, and the balloon will lose its ability to hover.
One solution to this problem is shown in U.S. Pat. No. 4,547,167 to Bergmann, which discloses a plurality of paper counterbalancing strips having perforated sections which may be torn off to incrementally decrease the weight of the ballast as the buoyancy of the balloon decreases. The sections are arranged symmetrically on the balloon, and removed in a preselected order to maintain the balloon in its proper attitude.
Such an apparatus has several drawbacks. Because Mylar balloons lose their buoyancy very slowly, the incremental changes caused by removing pairs of the ballast sections can be too great a decrease in the counterweight, thereby increasing the loft of the balloon and requiring it to be tethered. The strips also interfere with the markings or insignias on the balloon face, which are often the principal reason for displaying the balloon. The strips cannot subsequently be reused on other balloons, and cannot easily be completely removed and later reapplied to the same balloon if it is desired to utilize the full loft of the balloon for a period.
The Calderwood '661 patent referenced above provides one means to remedy some of these problems. The Calderwood '661 devices utilizes a container which may be filled with a liquid such as water. The container defines a small aperture through which the liquid may be introduced into the container by suction after the container is deformed, and small amounts of the liquid may be ejected from the container to achieve a precise counterweight by similarly deforming the container. The aperture is small enough that surface tension prevents the fluid from escaping, but permits the user to adjust the ballast weight continuously rather than incrementally.
The Calderwood '661 device also presents some problems. Due to the size and weight of the container, the amount of water necessary to permit controllable weight adjustments, and the weight of the mounting assembly, the device has proven useful with larger volume balloons having greater lifting capacity, but not the Mylar type balloons such as are sold for novelty or greeting purposes. Similarly, a balance mass is necessary to correct the attitude of the balloon, which additionally limits the utility of the device to larger balloons. The apparatus also has a tendency to lose ballast if jarred or handled carelessly, and the user must then recalibrate the liquid counterweight to regain the proper equilibrium, a process that is time consuming.
Moreover, devices similar to both the Calderwood '661 and Bergmann '167 ballast apparatuses require periodic or frequent readjustment by the user, and do not permit truly unrestrained continuous free flight over periods equal to the duration of a Mylar balloon's sustained buoyancy.